1. Field of the Invention
This invention pertains generally to devices for administering powdered medicament to a patient, and more particularly to an apparatus for aerosolizing powdered medicament internal to a medicament storage receptacle containing a prepackaged measured dose of medicament.
2. Description of the Background Art
The aerosolization and delivery of selected medicaments for inhalation deposition within the respiratory airways of the human lung is an important means of treating patients having lung diseases. Currently, aerosol therapy utilizes one of three primary methods for generation of respirable medicinal aerosols, namely (a) nebulization of aqueous solutions or suspensions containing the medicine using a pneumatic or ultrasonic nebulization nozzle, (b) forced dispersion of a spray of a volatile chlorofluorocarbon (such as Freon.RTM.) liquid propellant containing the medicine as particles in liquid solution or suspension using a metered-dose inhaler (MDI), and (c) dry aerosolization of a medicament powder.
The first two methods are extremely effective in the treatment of patients with lung diseases, and the MDI is particularly popular with patients because it is small, pocket-sized, and portable. Furthermore, the MDI does not require a separate supply of compressed gas or electrical power for operation, so it can be effectively used anywhere when aerosol treatment is required. Unfortunately, the use of chlorofluorocarbons is being discontinued as a result of concern over the damage that has been reported to the protective ozone shield found in the stratosphere of the earth's atmosphere. The popular MDI may be eliminated if no suitable propellant is developed.
Therefore, the most likely suitable alternative to the MDI lies with dry aerosolization of a medicament powder that has been finely divided into particles that are small enough to be in the respirable size range. There are various existing designs and types of powder aerosol delivery devices and powder inhalers, but they have not been popular for therapy because of many operational problems. Some dry powder aerosolization devices require electrical power and compressed air or gas to operate. The small portable powder inhalers that have been designed have a variety of operational shortcomings, so that their use is not popular. The primary problem with such devices is their inability to deliver a consistent dose of medicine to the patient. The amount of powdered medicament entrained in a flow of air varies, in many cases medicament which should be administered to the patient is retained within the device and wasted, aerosolization density varies, and considerable effort must be exerted by the patient in generating an air flow to entrain the medicament. Some powder delivery devices move the medicament from a storage region to an aerosolization region for entrainment. As a result of mechanical handling of the medicament, any exposed surface inside the device that has contact with the medicament will acquire some residual medicament resulting in accumulated losses. While some powder delivery devices have minimized the handling of medicament by the use of a disk-shaped configuration with "blister" packs, problems still exist due to the medicament falling or being moved into a separate aerosolization region. Other devices may fail to provide a powder aerosol of respirable particle size due to air velocity being insufficient for full aerosolization, or due to portions of the aerosolization region not receiving air whatsoever.
Therefore, there is a need for a device which can generate a measured and reproducible dosage of respirable aerosol of the desired medicament powder with each puff of the powder inhaler, without waste of medicine, losses in the dispensing device, or strenuous effort by the patient. The present invention solves those needs and eliminates the deficiencies in existing powder inhalation devices.